Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft drives the generator rotor either directly (“directly driven”) or through the use of a gearbox.
An important auxiliary system generally provided on wind turbines is the pitch system. Pitch systems are employed for adapting the position of a wind turbine blade to varying wind conditions. A pitch system normally comprises a slew bearing comprising an outer ring, an inner ring and, between these two rings, one or more rows of rolling elements which allow both rings to rotate relative to each other.
In some cases pitch bearings may further comprise a gear which meshes with a drive pinion. When gusts of wind impinge on a blade, the wind forces may act to substantially bend the blade. Such bending has an effect on the loads transmitted to the bearing. This way, some of the rolling elements of the bearing may carry larger loads than others, thus deforming the pitch bearing. The loads acting on the bearing may cause the linear contact and load transmission between the driven gear (crown) and the drive pinion to be shifted from its nominal position and the gear meshing (and the bearing) of such systems may thus suffer deformations.
One way to tackle such unevenly distributed loads would be to make the bearing larger in order to increase its stiffness and to limit its deformation. However, this would add weight and cost to the design.
Document U.S. Pat. No. 7,780,417 describes a stiffening element provided between the rotor blade and the pitch bearing, connected to the same via joining means. But this kind of solution can be rather complicated and expensive.
Thus, there still exists a need to provide a robust electromechanical pitch bearing which reduces its deformations during operation of the wind turbine and is cost-effective.